The term thermoforming defines a process in which a film or sheet of a thermoplastic polymer is heated in a controlled manner to temperatures close to the glass transition temperature of the material and then, with the help of air flow, vacuum, mechanical or even combined actions, the plastic sheet is deformed into a defined geometric shape.
Under this deformation, it is cooled down to room temperature, so that the shape achieved in three dimensions retains its form at the temperature of use. This process in the industry is carried out in continuous operation, which requires multiple process steps called stations. These stations are arranged consecutively in order to achieve the final product in the most efficient way possible.
Film dragging system.
The function of this system is to be able to give the rewound film the movement synchronised with the process from which the packaging will be obtained, from the moment it is unwound in the initial part of the machine called material entry into the machine. It is then held by a system of chains or servo-controlled automatic feed.
At this point, it is important to check that the film is mounted in the correct position as it has a marking that defines the side where the lidding material is to be welded later on.
When the polymeric material is taken by the conveyor system to the pre-heating station, the thermal process begins. In this station, the film is heated until it has the right consistency so that it can take the shape of the container when it goes to the thermoforming station. Although this phase of the process seems simple, it is important to mention that it must be perfectly controlled to achieve the right temperature in the film, above the glass transition temperature (Tg) and close to the crystallisation point (Tm), both temperatures depending on the type of material. Before the film reaches the point where the thermoforming of the container will take place, the film must not be too hot, as it would flow and "sag", losing important chemical and physical characteristics to continue the process, but it must not be too cold either, as in this case, the desired geometry would not be achieved or we would have problems with the uniform distribution of the polymer in the container, taking away its aesthetic characteristics and mechanical resistance.
This station is the most important part of the process, not only because it is where the container is formed in a defined way, but also because of the complexity it represents, as it is where the different mechanical, pneumatic, electrical, etc. drives, which are precisely adjusted to achieve the required result, are carried out in a coordinated manner.